Viral vector for the targeted transfer of genes in the brain and spinal cord

ABSTRACT

The invention relates to novel peptides, polypeptides or proteins which bind specifically to brain cells and/or to the spinal cord. The peptides, polypeptides, or proteins can be components of a viral capsid and can be used to lead a recombinant viral vector selectively to the brain and/or spinal cord after systemic administration to a subject and to ensure tissue-specific expression of one or more transgenes there. The invention also relates to a recombinant viral vector, preferably an AAV vector, which comprises a capsid containing at least one of the claimed peptides, polypeptides, or proteins and which comprises at least one transgene packaged in the capsid. Said viral vector can be used, in particular for the therapeutic treatment of a disease or disorder of the brain and/or spinal cord. The invention further relates to cells and pharmaceutical compositions that comprise the viral vector according to the invention.

RELATED APPLICATIONS

This application is the National Stage of International patentapplication No. PCT/EP2015/058123, filed Apr. 15, 2015, which is herebyincorporated by reference in its entirety, and which claims priority toGerman Patent application No. 102014207498.3, filed Apr. 17, 2014.

SEQUENCE LISTING

The sequences listed in the accompanying Sequence Listing are presentedin accordance with 37 C.F.R. 1.822. The Sequence Listing is submitted asan ASCII computer readable text file, which is incorporated by referenceherein.

The invention relates to novel peptides, polypeptides or proteins whichspecifically bind to cells of the brain and/or the spinal cord. Thepeptides, polypeptides or proteins can be part of a viral capsid, andthey can be used for guiding a recombinant viral vector selectively tothe brain and/or spinal cord after systemic administration to a subject,where it provides for a tissue-specific expression of one or moretransgenes. The invention therefore also relates to a recombinant viralvector, preferably an AAV vector, comprising a capsid containing atleast one of the peptides, polypeptides or proteins of the invention andat least one transgene which is packaged within the capsid. The viralvector is particularly suitable for the therapeutic treatment of adisease or functional disorder of the brain and/or the spinal cord. Theinvention further relates to cells and pharmaceutical compositionscomprising the viral vector of the invention.

BACKGROUND OF THE INVENTION

The gene therapeutic treatment by use of viral vectors is a promisingtreatment option for diseases that do not respond or do not sufficientlyrespond to conventional treatment. This approach is based on theintroduction of therapeutic genes into the organism to be treated usingviruses which have been modified to include the sequence of therespective gene in their genome. Viral vectors which have been used forgene therapy in gene therapeutic approaches are based on retroviruses,lentiviruses, adenoviruses and adeno-associated viruses.

Adeno-associated viruses (AAV) are promising candidates for use inclinical practice because they are considered as relatively safe. AAVvectors are capable of introducing a transgene into a tissue andexpressing same stably and efficiently. At the same time, these vectorsdo not possess any known pathogenic mechanism [1]. The AAV vectors ofserotype 2 (AAV2) are of particular importance for clinical use, andthese vectors have been examined particularly well. After introductionby AAV vectors, the transgenes can be present within the transfectedcell in different forms, for example as episomal, single-stranded ordouble-stranded DNA. Concatemeric forms of DNA were also found intransduced cells.

The genome of AAV2 is a linear, single-stranded DNA molecule ofapproximately 4700 nucleotides in length, and it comprises invertedterminal repeats (ITRs) at both ends. The genome further comprises twolarge open reading frames which are referred to as replication region(rep) and capsid region (cap). The replication region encodes proteinswhich are required in connection with virus replication. In contrast,the capsid region encodes the structural proteins VP1, VP2 and VP3 whichmake up the icosahedral capsid of the virus.

As most of the vectors which can be used in gene therapy and which areknown in the state of the art, wild-type AAV vectors, e.g. the disclosedAAV2 vectors, do not possess sufficient specificity for a specifictissue but instead infect a wide variety of cell types. Upon systemicadministration of these wild-type vectors, the target tissue isinsufficiently transduced, and severe immune reactions have to beexpected in the treated patient due to the undesired transduction ofother tissues. Progress has been made with the development of viralvectors having an increased specificity for particular organs by usingpeptide ligands that are capable of guiding the vectors to specificorgans [2-3]. It could be shown that specific peptide ligands providefor a “homing” to different organs such as the brain.

Reference [4] describes a method that allows for the screening ofcapsids of AAV2 with modified tropism in randomized peptide libraries.From these libraries, vectors can be isolated that specificallytransduce a desired cell type in vitro. However, it has been found thatcapsids selected in this way are often unsuitable for being used in vivosince the required specificity is missing in an animal model [5].

From the clinical perspective, the brain is an extremely relevant organ,since it is the starting point of a variety of neurological diseases.Considerable efforts have been made to make this organ accessible forgene therapeutic interventions [6-12]. However, the blood brain barrier,which is composed of endothelial cells, pericytes and astrocytes andwhich seals the brain off from circulating particles, toxins and signalcompounds, represents a barrier that cannot be passed by normal vectorsystems. Since suitable vector systems that transduce the brain withsufficient efficiency after intravenous application are not available sofar, present gene therapy vectors are normally injected directly intothe brain [13] which is associated with a higher risk for the patient.The possibility of making the blood brain barrier permeable for a shorttime, e.g. by ultrasound [14] or by chemical agents [7] is also regardedas very risky.

Accordingly, there is a high demand for agents, which are capable ofmodulating the tropism of viral vectors, thereby providing for asufficient cell or tissue specificity which renders possible a targetedtransport of a viral vector to tissues of the brain or spinal cord. Suchvectors can provide for the specific expression of therapeutic genes inthese tissues, thereby effectively treating diseases and/or functionalconditions of the brain and the spinal cord.

The present invention provides viral vectors for the targeted genetransfer into the brain and spinal cord. The viral vectors of thepresent invention express on their capsid surface so far unknown aminoacid sequences that are specifically recognized in vivo by receptors onthe neurons of the brain and the endothelial cells of the blood vesselsof the brain and spinal cord. In this way, the viral vectors of thepresent invention, after systemic administration to a subject,specifically transduce the tissues in the brain and spinal cord.

The viral vectors of the present invention further enable a strong andlong persisting expression of a transgene in the neurons of the brainand in the endothelial cells of the blood vessels of the brain andspinal cord. Therefore, the vectors are particularly suitable for thegene therapeutic treatment of defined diseases or conditions of thebrain and spinal cord. It has been furthermore found that the AAVvectors produce only a slight immune reaction after transfection in thehost, and they are therefore particularly suitable for gene therapy.

DESCRIPTION OF THE INVENTION

In the present invention, various sequences that are specific for thecentral nervous system, i.e. for the brain and spinal cord, wereidentified by selection in a randomized AAV2 heptamer peptide library. Aheptamer having particular specificity for the brain was peptide NRGTEWD(SEQ ID NO:1). Based on this sequence, the recombinant viral vectorrAAV2-NRGTEWD (SEQ ID NO:1) was produced which expresses the peptidesequence NRGTEWD (SEQ ID NO:1) as a partial sequence of the capsidprotein VP1. Subsequently, vector rAAV2-NRGTEWD (SEQ ID NO:1) wasadministered intravenously to mice and a clear specificity of the vectorfor the central nervous system could be observed both in vitro and invivo. Both neurons of the brain and endothelial cells of the bloodvessels of the brain and the spinal cords were transfected by thevector. The specificity was confirmed by staining with CD31 as describedin the present examples.

A further group of peptides, which also showed specificity for the brainand spinal cord, encompassed peptides ADGVQWT (SEQ ID NO:2), DDGVSWK(SEQ ID NO:3), SDGLTWS (SEQ ID NO:4) and SDGLAWV (SEQ ID NO:5). Thesepeptides contained the general motif XDGXXWX (SEQ ID NO: 6).

The present invention therefore provides different peptide sequenceswhich are specific for the brain and spinal cord and which areparticularly suitable for guiding therapeutic agents, such as viralvectors, to the brain or spinal cord of a subject to be treated,respectively.

In a first aspect, the present invention therefore relates to a peptide,polypeptide or protein which specifically binds to cells of the brainand/or spinal cord, wherein the peptide, polypeptide or proteincomprises the amino acid sequence of SEQ ID NO:1 or a variant thereof,wherein the variant differs from the amino acid sequence of SEQ ID NO:1by modification of a maximum of one amino acid. The peptide, polypeptideor protein of the present invention preferably binds to endothelialcells and/or neurons of the brain or spinal cord.

In a second aspect, the present invention relates to a peptide,polypeptide or protein, which specifically binds to cells of the brainand/or spinal cord, wherein the peptide, polypeptide or proteincomprises the general amino acid sequence of SEQ ID NO:6. In aparticularly preferred embodiment, the peptide, polypeptide or proteincomprises one of the sequences of ADGVQWT (SEQ ID NO:2), DDGVSWK (SEQ IDNO:3), SDGLTWS (SEQ ID NO:4) or SDGLAWV (SEQ ID NO:5) or a variantthereof, wherein the variant differs from the respective amino acidsequence of SEQ ID NO:2-5 by modification of a maximum of one aminoacid. The peptide, polypeptide or protein of the present inventionpreferably binds to endothelial cells and/or neurons of the brain orspinal cord.

In the context of the present disclosure, the tern “peptide” refers to alinkage of 2-10 amino acids which are connected to each other by apeptide bond. The term “polypeptide” refers to a linkage of 11-100 aminoacids that are connected to each other by a peptide bond. Polypeptideswith more than 100 amino acids are referred to herein as a “protein.”

In a particularly preferred embodiment according to the invention, thepeptide sequence of SEQ ID NO:1 or a variant thereof or SEQ ID NO:2-6 ora variant thereof, which are specific for the brain and spinal cord, isa part of a capsid protein of a virus. This means that the sequence,which is specific for the brain and spinal cord, is present as part of acapsid protein of the virus. To produce such capsid proteins, acorresponding nucleotide sequence which codes for the peptide is clonedinto the region of the virus genome which codes for a capsid protein ofthe virus. If the sequence, which is specific for the brain and thespinal cord, respectively, is expressed as part of a capsid protein, itcan be presented in many copies across the surface of the viral vector.

The capsid protein is preferably one which is derived from anadeno-associated virus (AAV). The AAV can be any of the serotypesdescribed in the prior art, wherein the capsid protein is preferablyderived from an AAV of one of the serotypes 2, 4, 6, 8 and 9. A capsidprotein of an AAV of serotype 2 is particularly preferred.

The capsid of the AAV wild-type is made up of the capsid proteins VP1,VP2 and VP3, which are encoded by the overlapping cap region. All threeproteins have the same C-terminal region. The capsid of AAV comprisesabout 60 copies of the proteins VP1, VP2 and. VP3, expressed in a ratioof 1:1:8. If a nucleotide sequence coding for one of the peptides, whichis specific for the brain and the spinal cord, respectively, and whichis described herein is cloned at the C-terminus into the reading frameof VP1 (i.e., in the region that is identical in all three proteins), itcan be expected that theoretically 60 of the specific peptides can befound on the capsid surface.

If an AAV vector in the context of the present invention is modified,the nucleotide sequence coding for the peptide which is specific for thebrain is then cloned into the cap region at the 3′ end of the genome.The sequence encoding the peptide being specific for the brain andspinal cord, respectively, can be cloned into the genomic sequence ofone of the capsid proteins VP1, VP2 or VP3. The capsid proteins of AAV2are illustrated by way of example in SEQ ID NO:7 (VP1), SEQ ID NO:8(VP2), and SEC ID NO:9 (VP3).

In one particularly preferred embodiment according to the invention, thesequence encoding the peptide, which is specific for the brain andspinal cord, respectively, is cloned into the reading frame of a VP1gene, preferably in the VP1 gene of AAV2 shown in SEQ ID NO:7. It shouldbe noted in this case that the insertion of the cloned sequence does notlead to any change of the reading frame, nor to a premature terminationof translation. The methods required for the above will be readilyapparent to a person skilled in the art.

In all three capsid proteins of AVV, sites have been identified at whichpeptide sequences can be inserted for the homing function [15-20]. Amongother things, the arginine which occurs in the VP1 of AAV2 at position588 (R588) has specifically been proposed for the insertion of a peptideligand [21-22]. This amino acid position of the viral capsid isapparently involved in the binding of AAV2 to its natural receptor. Ithas been suggested that R588 is one of four arginine residues whichmediates the binding of AAV2 to its natural receptor [23-24]. Amodification in this region of the capsid weakens the natural tropism ofAAV2, or eliminates it completely.

Accordingly, it is particularly preferred according to the inventionthat the peptide sequence of SEQ ID NO:1 or a variant thereof or of SECID NO:2-6 or a variant thereof is present in inserted form in the regionof the amino acids 550-600 of the VP1 protein of AAV2, in particular ofthe VP1 protein of SEQ ID NO:7. Even more preferably, the peptidesequence is present in inserted form in the region of amino acids560-600, J570-600, 560-590, 570-590 of the VP1 protein.

Thus, the peptide sequence of SEQ ID NO:1 or a variant thereof or SEQ IDNO:2-6 or a variant thereof can adjoin, by way of example, directlybehind one of the following amino acids of the VP1 protein, particularlythe protein of SEQ ID NO:7: 550, 551, 552, 553, 554, 555, 556, 557, 558,559, 560, 561, 562, 563, 564, 565, 566, 567, 568, 569, 570, 571, 572,573, 574, 575, 576, 577, 578, 579, 580, 581, 582, 583, 584, 585, 586,587, 588, 589, 590, 591, 592, 593, 594, 595, 596, 597, 598, 599 or 600.

It is particularly preferred that the amino acid sequence of SEQ ID NO:1or a variant thereof or SEQ ID NO: 2-6 or a variant thereof follows theamino acid 588 of the VP1 protein of SEQ ID NO:7, as shown in theexamples. It is possible in this case that one or more, and particularlyup to 5 (i.e., 1, 2, 3, 4 or 5) amino acids which are the result of thecloning are situated between the arginine residue at position 588 andthe first amino acid of the peptide of the invention or the variantthereof. Likewise, one or more, and particularly up to 5 (i.e., 1, 2, 3,4, or 5) amino acids can be situated behind the last amino acid of thepeptide of the invention or the variant thereof.

The sites and regions in the amino acid sequence of the capsid proteinindicated above for VP1 apply analogously to the capsid proteins VP2 andVP3 of AAV2. Because the three capsid proteins VP1, VP2 and VP3 of AAV2differ only by the length of the N-terminal sequence and accordinglyhave an identical C-terminus, a person skilled in the art will have noproblem making a sequence comparison to identify the sites indicatedabove, for the insertion of the peptide ligands, in the amino acidsequences of VP1 and VP2. As such, the amino acid 588 in VP1 correspondsto position VP1 of VP2 (SEQ ID NO: 8) and position R386 of VP3 (SEQ IDNO:9), respectively.

SEQ ID NO:10 shows an example of the sequence of the VP1 protein of AAV2after introduction of the peptide sequence of SEQ ID NO:1. Due to thecloning, the capsid protein has two additional amino acids which do notoccur in the native sequence of the VP1 protein of AAV2. As such, thepeptide sequence of SEQ ID NO:1 is flanked at its N-terminus by aglycine in position 589, and at its C-terminus by an alanine in position597. In addition, the asparagine at position 587 of the native sequenceis replaced with a glutamine.

In one particular embodiment, the present invention therefore alsorelates to a capsid protein which comprises or consists of:

-   (a) the amino acid sequence of SEQ ID NO:10;-   (b) an amino acid sequence which is at least 80%, and preferably 90,    95 or 99%, identical to the amino acid sequence of SEQ ID NO:10 and    furthermore (i) comprises the amino acid sequence of SEQ ID NO:1    or (ii) an amino acid sequence, which differs from. the amino acid.    sequence of SEQ ID NO:1 by modification. of one amino acid; or-   (c) a fragment of one of the amino acid sequences defined in (a) or    (b).

In a further aspect, the invention is directed to a viral capsid, whichcomprises a peptide, polypeptide or protein which specifically binds tocells of the brain or spinal cord, respectively, and comprises the aminoacid sequence of SEQ ID NO:1 or a variant thereof or SEQ ID NO:2-6 or avariant thereof.

Furthermore, the present invention also provides a nucleic acid encodinga peptide, polypeptide or protein as described above. A nucleic acidwhich encodes a capsid protein which comprises a peptide, polypeptide orprotein according to the invention as described above, is likewiseprovided. Preferably, the nucleic acid coding for the capsid proteincomprises the nucleotide sequence of SEQ ID NO:11 or a nucleotidesequence derived from the same with at least 80% sequence identity. Aplasmid comprising such a nucleic acid is also provided.

In yet another aspect, the invention relates to a recombinant —i.e.,produced by means of genetic engineering techniques—viral vector, havinga capsid and at least one transgene packaged therein, wherein the capsidcomprises at least one capsid protein having the amino acid sequence ofSEQ ID NO:1 or a variant thereof or SEQ ID NO:2-6 or a variant thereof.The recombinant viral vector can be a recombinant AAV vector—forexample, of serotype 2, 4, 6, 8, 9. AAV vectors of serotype 2 areparticularly preferred.

The different AAV serotypes differ mainly by their natural tropism. Assuch, wild-type AAV2 binds more readily to alveolar cells, while AAV5,AAV6 and AAV9 mainly infect epithelial cells. A person skilled in theart can take advantage of these natural differences in the specificityof the cells to further enhance the specificity mediated by the peptidesaccording to the invention for certain cells or tissues. At the nucleicacid level, the various AAV serotypes are highly homologous. Forexample, serotypes AAV1, AAV2, AAV3 and AAV6 are 82% identical on thenucleic acid level [25].

The capsid of the viral vectors according to the invention comprises oneor more transgenes. A gene which has been introduced by geneticengineering into the genome of the vector is termed a transgene. Thetransgene (or transgenes) can be DNA or RNA. Preferably, it issingle-stranded DNA (ssDNA) or double-stranded DNA (dsDNA), such asgenomic DNA or cDNA. Preferably, the transgene which is to betransported with the aid of the recombinant viral vector according tothe invention is a human gene. Suitable transgenes include, for example,therapeutic genes to replace a dysfunctional gene in patients. They canalso be genes which are not expressed in the corresponding targettissue, or are only expressed to an insufficient extent. In onepreferred embodiment, the transgene which is expressed from the viralvector according to the invention is a.

The vectors of the present invention can be used, amongst others, forthe treatment of Multiple Sclerosis (MS). In this case, the transgenecan be, e.g. a gene which encodes a membrane protein or a tight junctionprotein, such as for claudin and occludin. Preferably the transgene is agene from the family of claudins, e.g. the gene encoding claudin 1. Theoverexpression of one of such genes could be helpful for “sealing” theblood brain barrier that is damaged by the disease.

In addition, a gene can be used for the treatment of MS which encodes achemokine antagonist. For example, a negative-dominant mutant of thechemokine CCL2 (aka MCP1) can be expressed which is referred to as“CCL2-7ND”. CCL2 provides for the attraction of immune cells to the siteof inflammation which in the case of MS results in the inflammatorydegradation of the myelin sheaths of neurons. In contrast, thedominant-negative variant “CCL2-7ND” forms dimers and blocks thereceptor CCL2, thereby interfering with the signal cascade such that theimmune cells are no longer attracted by the neurons.

For the treatment of Alzheimer's Disease, e.g. the gene encodingneuraminidase 1 (NEU1), neprilysine or cholesterol 24 hydroxylase can beoverexpressed which leads to the degradation of amyloid β plaques andtherefore can contribute to an amelioration of the state of disease.

Parkinson's disease can be treated by vector-mediated overexpression ofe.g. the neurotrophic factors of glia cells (GDNF), the aromatic L-aminoacid decarboxylase, the tyrosine hydroxylase or the GTP cyclohydrolase1, wherein a positive influence on the dopaminergic system can beexpected. A treatment of the spinal muscle atrophy can be achieved, e.g.by expression of the protein SMN (survival of motor neuron).

For the therapy of a lysosomal storage disease, the expression ofglucuronidase, e.g. β-glucuronidase, as a transgene by use of thevectors of the present invention would be promising. In a furtherembodiment, the transgene encodes a radio-protective protein such as aradioprotective enzyme. A major limitation of radiotherapy in thetreatment of cancer is the radiation-induced damage to the normaltissue, which often makes a reduction in radiation dose, an interruptionof the treatment regimen, or even a complete abandonment of this form oftherapy necessary. The brain is a particularly radiosensitive organ,which is why primary tumors there often can only be treated to a limitedextent with radiotherapy, and diffuse tumor growth usually cannot betreated at all with radiotherapy. With the help of the vectors of thepresent invention, the healthy tissue surrounding the malignant tissuecan be protected by targeted expression of radioprotective proteins. Inone preferred embodiment, the transgene which is introduced into thehealthy brain tissue is a manganese superoxide dismutase (MnSOD) whichcatalyzes the conversion of superoxide anions—one of the criticalfactors in radiation-induced toxicity—to hydrogen peroxide. A furtherembodiment proposed here involves the kinase domain of the Ataxiatelangiectasia mutant (ATM) gene, which contributes to the repair of DNAdamage caused by radiation. In a further preferred embodiment, bothgenes are introduced by means of the presently described vectors intothe patient undergoing treatment.

The viral vectors of the present invention are particularly suitable foruse in a method of therapeutic treatment of diseases of the brain and/orspinal cord. Diseases of the brain and spinal cord, respectively, in thesense of the present invention comprise genetically causedleukodystrophies, such as adrenoleukodystrophy, Cananvan disease, Krabbedisease, metachromatic leukodystrophy, Pelizaeus-Merzbacher disease andAlexander disease; neurodegenerative diseases such as amyotrophiclateral sclerosis, Alzheimer's disease, Parkinson's disease,Huntington's disease and Pick's disease; chronic-inflammatory diseasesof the central nervous system such as Multiple Sclerosis andGuillain-Barré syndrome and lysosomal storage diseases such as ceroidlipofuscinosis and Fabry disease. In a particularly preferredembodiment, the viral vectors of the present invention are for thetherapeutic treatment of neurodegenerative diseases such as Alzheimer'sdisease, Parkinson's disease or Huntington's disease.

In yet another embodiment, the transgene encodes an antitumor agent,such as a tumor suppressor protein, or an immunomodulator, such as acytokine (e.g. interleukin 1 to 4, gamma-interferon, p53), which isintended to be transported selectively to a brain tumor or a tumor ofthe spinal cord of the patient.

The vectors can also be used to transport antisense-RNA, ribozymes, orthe like into cells or tissues of the brain or spinal cord. Furthermore,vectors according to the invention can also comprise transgenes encodingsecretory proteins that are intended for being released to themicrovasculature of the brain or spinal cord. Such secretory proteinscan be effective, e.g. as anti-inflammatory agents.

As used herein, the term “subject” indicates any human or animalorganism that can be infected by AAV vectors. Preferably, the subjectbeing treated is a mammal such as a human, a primate, a mouse or a rat.In one preferred embodiment, the subject to be treated is a human. Aftertransfection into the subject, the vector brings about a site-specificexpression of the transgene in the cells of the brain or spinal cord.

The transgene can be present in the viral vector in the form of anexpression cassette, which in addition to the sequence of the transgeneto be expressed comprises further elements necessary for expression,such as a suitable promoter which controls the expression of thetransgene after infection of the appropriate cells. Suitable promotersinclude, in addition to the AAV promoters, e.g. the cytomegalovirus(CMV) promoter or the chicken beta actin/cytomegalovirus hybrid promoter(CAG), an endothelial cell-specific promoter such as the VE-cadherinpromoter, as well as steroid promoters and metallothionein promoters. Inone particularly preferred embodiment, the promoter used in the vectorsaccording to the invention is a CAG promoter. In one particularlypreferred embodiment, the transgene according to the invention comprisesa brain-specific promoter which is functionally linked to the transgeneto be expressed. In this way, the specificity of the vectors accordingto the invention for the brain can be further increased. As used herein,a brain-specific promoter is a promoter whose activity in brain tissueis at least 2-fold, 5-fold, 10-fold, 20-fold, 50-fold or 100-fold higherthan in a cell which is riot a brain cell. Preferably, this promoter isa human promoter. The expression cassette can also include an enhancerelement for increasing the expression levels of exogenous protein to beexpressed. Furthermore, the expression cassette can includepolyadenylation sequences, such as the SV40 polyadenylation sequences orpolyadenylation sequences of bovine growth hormone.

The viral vectors according to the invention can, preferably as part ofone of their capsid proteins, comprise a peptide sequence of any of SEQID NO:1-5. Alternatively, variants of the amino acid sequence of SEQ IDNO:1-5 can be used, the same differing from the amino acid sequence ofSEQ ID NO:1-5 by the modification of one amino acid. The modificationcan be a substitution, deletion or insertion of amino acids, as long asthe variant retains the ability to mediate, as part of the capsid, thespecific binding of the vector to the receptor structures of cells ofthe brain and/or spinal cord. The invention therefore also extends tovariants of the sequence of SEQ ID NO:1-5 in which the C- or N-terminalamino acid has been changed. These variants have a sequence identity ofmore than 85% to the amino acid sequence shown in SEQ ID NO:1-5 when thesequences are compared using the programs GAP or BESTFIT. These computerprograms for determining amino acid sequence identity are sufficientlyknown in the art.

The variant of the sequence of SEQ ID NO:1-5 can be based on thesubstitution of one amino acid—that is, one amino acid can be replacedwith another amino acid. Preferably, the substitution by which thevariants differ from one of the amino acid sequences in SEQ ID NO:1-5 isa conservative substitution, i.e., a substitution of one amino acid byan amino acid of similar polarity which gives the peptide similarfunctional properties. Preferably, the substituted amino acid is fromthe same group of amino acids as the amino acid which is used for thereplacement. For example, a hydrophobic residue can be replaced withanother hydrophobic residue, or a polar residue by another polarresidue. Functionally similar amino acids which can be exchanged foreach other by a conservative substitution include, for example,non-polar amino acids such as glycine, valine, alanine, isoleucine,leucine, methionine, proline, phenylalanine, and tryptophan. Examples ofuncharged polar amino acids are serine, threonine, glutamine,asparagine, tyrosine, and cysteine. Examples of charged, polar (acidic)amino acids include histidine, arginine and lysine. Examples of charged,polar (basic) amino acids include aspartic acid and glutamic acid.

As variants of the amino acid sequences shown in SEQ ID NO:1-5 areregarded also those amino acid sequences in which an amino acid has beeninserted. Such insertions can in principle be carried out as long as theresulting variant retains its ability to bind specifically to cells ofthe brain or spinal cord. In addition, in the present context, thoseproteins in which one of the two N-terminal amino acids of SEQ ID NO:2is missing are considered to be variants of the amino acid sequenceshown in SEQ. ID NO:1-5. This requires in turn that the correspondinglydeleted variant binds specifically to cells of the brain or spinal cord.

Also encompassed by the invention are specific variants of the aminoacid sequences shown SEQ ID NO:1-5 which were structurally modified atone amino acid, for example by introducing a modified amino acid.According to the invention, these modified amino acids can be aminoacids that have been modified by biotinylation, phosphorylation,glycosylation, acetylation, branching and/or cyclization.

Viral vectors with capsids that comprise one of the peptide sequencesaccording to the invention, or a variant thereof as defined above,specifically bind to cells of the brain and/or spinal cord. As usedherein, a “specific” binding of the vectors according to the inventionmeans that the vectors accumulate after systemic administration mainlyon or in the cells of the brain and/or spinal cord. This means that morethan 50% of the originally administered vector genomes accumulate in thearea of the cells of the brain and/or spinal cord, while less than 50%accumulate in other cells or tissues (such as in the spleen or liver),or in the area thereof. It is preferred that more than 60%, 70%, 80%,90%, 95%, or even more than 99% of the originally administered vectorgenomes accumulate in, or in the area of, the cells of the brain and/orspinal cord. Specific binding of the vectors can also be determined viathe expression of the transgene. In the case of viral vectors which bindspecifically to cells of the brain and/or spinal cord, more than 50% ofthe total expression of the transgene occurs in, or in the region of,the brain and/or spinal cord, while less than 50% of the expression canbe observed in, or in the region of, other tissues. It is preferred,however, that more than 60%, 70%, 80%, 90%, 95%, or even more than 99%of the total measured expression of the transgene occurs in, or in theregion of, the brain and/or spinal cord.

A person skilled in the art will easily be able to determine thespecific binding of the vectors according to the invention to cells ofthe brain and/or spinal cord and the expression of the transgeneintroduced using the vectors. Methods for measuring the specificity oftransduction and expression, suitable for this purpose, are shown in theexamples below.

It is also preferable according to the invention that vectors whosecapsids comprise variants of the amino acid sequences shown in SEQ IDNO:1-5 have at least about 50% of the binding activity of acorresponding viral vector whose capsid has the amino acid sequenceshown in SEQ ID NO:1-5. It is even more preferred that the variants haveabout 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% of the bindingactivity of a corresponding viral vector whose capsid has the amino acidsequence shown in SEQ ID NO:1-5. The binding activity of the vectors canbe measured with the aid of in vitro assays, as described in theincluded examples.

Preferably, the binding activity of the vectors according to theinvention, as can be determined by distribution of the vector genomes orexpression of the transgene, for cells of the brain and/or spinal cordis at least 2-fold, 5-fold, 10-fold, 20-fold, 50-fold, 75-fold,100-fold, 150-fold, 200-fold, 250-fold, 500-fold, 600-fold, 700-fold,800-fold, 900-fold, 1000-fold, 2000 fold, 5000-fold, or 10,000-foldhigher than the binding activity for a control cell which is not a cellof the brain or spinal cord (such as a spleen or liver cell).

The invention also relates to a cell that comprises a peptide,polypeptide or protein according to the invention, a nucleic acidencoding the same, a plasmid comprising such a nucleic acid, or arecombinant AAV vector as described above. It is preferably a human cellor cell line.

In one embodiment, a cell has been, for example, obtained from a humansubject by biopsy and then transfected with the viral vector in an exvivo procedure. The cell can then be reimplanted in the subject, or besupplied in other ways to the subject—for example by transplantation orinfusion. The likelihood of rejection of transplanted cells is lowerwhen the subject from which the cell was derived is genetically similarto the subject to which the cell is administered. Preferably, therefore,the subject to whom the transfected cells are supplied is the samesubject from which the cells were previously obtained. The cell ispreferably a human cell of the brain or spinal cord, particularly aneuronal cell, an endothelial cell of a blood vessel. The cell to betransfected can also be a stem cell, such as a human adult stem cell. Itis particularly preferred according to the invention that the cells tobe transfected are autologous cells that have been transfected ex vivowith the viral vector according to the invention, for example therecombinant AAV2 vector described above. The cells are preferably usedin a method for treating a disorder or disease of the brain and/orspinal cord in a subject.

In another aspect, the invention relates to a method for producing anAAV vector in which a plasmid is used which encodes a capsid protein,the same comprising the amino acid sequence of SEQ ID NO:1 or a variantthereof. Alternatively, the vector can also comprise the amino acidsequence of SEQ ID NO:6, and in particular one of the amino acidsequences of SEQ ID NO:2-5 or a variant thereof. The basic method ofproducing recombinant AAV vectors comprising a transgene to be expressedis described in the prior art sufficiently [28]. HEK 293-T cells aretransfected with three plasmids. A first plasmid comprises the cap andrep regions of the AAV genome, but the naturally occurring invertedrepeats (ITRs) are missing. The cap region of this plasmid comprises agene encoding at least one modified capsid protein, i.e., a gene whichcomprises the peptide sequence according to the invention. A secondplasmid comprises a transgene expression cassette which is flanked bythe corresponding ITRs, which constitute the packaging signal. Theexpression cassette is therefore packaged into the capsid in the courseof the assembly of the viral particles. The third plasmid is anadenoviral helper plasmid, on which are encoded the helper proteins E1A,E1B, E2A, E4-orf6, VA, which are required for AAV replication in the HEK293-T cells. Alternatively, it is also possible to produce the AAVvectors of the present invention in insect cells. A correspondingprotocol is provided as an example in the below Example 6.

It was surprisingly found that the production of the recombinant vectorscan influence their specificity. In the course of the present inventionit was observed that vectors which have been produced in HEK293T cellsusing the protocol of Example 2 predominantly transfect endothelialcells of the blood vessels of the brain and spinal cord and only to aminor part neurons of the brain or the spinal cord. On the other hand,recombinant vectors which have been produced in Sf-9 cells using theprotocol of Example 6 predominantly transfect neurons and to a muchsmaller extent endothelial cells. This observation can be used forfurther increasing the specificity of transfection.

Conditions which allow the accumulation and purification of therecombinant vectors according to the invention are known in the art. Thevectors according to the invention can be purified, for example, by gelfiltration processes—for example using a Sepharose matrix—desalinated,and subsequently purified by filtration. Other purification methods canfurther comprise a cesium chloride or iodixanol gradientultracentrifugation process. Purification reduces potentiallydetrimental effects in the subject to which the adeno-associated viralvectors are administered. The administered virus is substantially freeof wild-type and replication-competent virus. The purity of the viruscan be checked by suitable methods such as PCR amplification.

In a further aspect, the invention provides a pharmaceutical compositioncomprising a viral vector of the present invention, particularly an AAVvector. The viral vector in this case is administered in atherapeutically effective amount to the patient, i.e., in an amountsufficient to considerably improve at least one symptom of thedysfunction or disease of the brain and/or spinal cord being treated, orto prevent the progression of the disease. A therapeutically effectiveamount of the viral vector of the present invention causes a positivechange in one of said symptoms, i.e. a change which renders thephenotype of the afflicted subject more similar to the phenotype of ahealthy subject that does not suffer from a disease of the brain and/orspinal cord.

In one preferred embodiment according to the invention, theadministration of the viral vector occurs in an amount which leads to acomplete or substantially complete healing of the dysfunction or diseaseof the brain and/or spinal cord. The pharmaceutical compositionaccordingly comprises a therapeutically effective dose of the vectoraccording to the invention. A therapeutically effective dose willgenerally be non-toxic for the subject who undergoes the treatment.

The exact amount of viral vector which must be administered to achieve atherapeutic effect depends on several parameters. Factors that arerelevant to the amount of viral vector to be administered are, forexample, the route of administration of the viral vector, the nature andseverity of the disease, the disease history of the patient beingtreated, and the age, weight, height, and health of the patient to betreated. Furthermore, the expression level of the transgene which isrequired to achieve a therapeutic effect, the immune response of thepatient, as well as the stability of the gene product are relevant forthe amount to be administered. A therapeutically effective amount of theviral vector can be determined by a person skilled in the art on thebasis of general knowledge and the present disclosure.

The viral vector is preferably administered in an amount correspondingto a dose of virus in the range of 1.0×10¹⁰ to 1.0×10¹⁴ vg/kg (virusgenomes per kg body weight), although a range of 1.0×10¹¹ to 1.0×10¹³vg/kg is more preferred, and a range of 5.0×10¹¹ to 5.0×10¹² vg/kg isstill more preferred, and a range of 1.0×10¹² to 5.0×10¹² is still morepreferred. A virus dose of approximately 2.5×10¹² vq/kg is mostpreferred. The amount of the viral vector to be administered, such asthe AAV2 vector according to the invention, for example, can be adjustedaccording to the strength of the expression of one or more transgenes.

The viral vector of the present invention, such as the preferred AAV2vector according to the invention, for example, can be formulated forvarious routes of administration—for example, for oral administration asa capsule, a liquid or the like. However, it is preferred that the viralvector is administered parenterally, preferably by intravenous injectionor intravenous infusion. The administration can be, for example, byintravenous infusion, for example within 60 minutes, within 30 minutesor within 15 minutes. It is further preferred that the viral vector isadministered locally by injection to the brain and/or spinal cord duringa surgery. Compositions which are suitable for administration byinjection and/or infusion typically include solutions and dispersions,and powders from which corresponding solutions and dispersions can beprepared. Such compositions will comprise the viral vector and at leastone suitable pharmaceutically acceptable carrier. Suitablepharmaceutically acceptable carriers for intravenous administrationinclude bacteriostatic water, Ringer's solution, physiological saline,phosphate buffered saline (PBS) and Cremophor EL™. Sterile compositionsfor the injection and/or infusion can be prepared by introducing theviral vector in the required amount into an appropriate carrier, andthen sterilizing by filtration. Compositions for administration byinjection or infusion should remain stable under storage conditionsafter their preparation over an extended period of time. Thecompositions can contain a preservative for this purpose. Suitablepreservatives include chlorobutanol, phenol, ascorbic acid andthimerosal. The preparation of corresponding formulations and suitableadjuvants is described, for example, in “Remington: The Science andPractice of Pharmacy,” Lippincott Williams & Wilkins; 21st edition(2005).

In a further aspect, the invention relates to a method for thetherapeutic treatment of a disorder or disease of the brain and/orspinal cord, wherein a viral vector according to the invention,preferably an AAV vector as described above, is administered to asubject. The vector comprises a capsid which has at least one capsidprotein containing the amino acid sequence of SEQ ID NO:1 or a variantthereof. Alternatively, the vector can also comprise an amino acidsequence of SEQ ID NO:6, in particular an amino acid sequence of SEQ IDNO:2-5 or a variant thereof. The viral vector further comprises atransgene, for example a therapeutic gene, which is useful for thetreatment of the disorder or the disease of the brain and/or spinalcord. After administration to the subject being treated, preferably bysystemic administration such as intravenous injection or infusion, forexample, the vector brings about the specific expression of the gene inthe cells of the brain and/or spinal cord.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows the in vivo selection method of the AAV-peptide libraryused according to the invention.

-   1.: Randomized AAV peptide library with approx. 1×10⁸ different    capsid variants;-   2.: Withdrawal of the target organ, 8 days after injection;-   3.: DNA isolation and amplification of viral DNA fragments via real    time PCR;-   4.: Cloning into peptide library plasmids for sequencing and    production of a secondary peptide library;-   5.: Co-transfection of HEK2931 cells; production of a secondary    peptide library;-   6.: secondary AAV peptide library for further rounds of selection;    contains pre-selected capsid variants;-   7.: intravenous injection of the peptide library into the mouse.

FIG. 2 shows the sequences of the brain-specific peptides identified bymeans of the selection method. The peptide with the sequence shown inSEQ ID NO:1 was identified in the fourth round of selection.

FIG. 3 shows the gene expression after intravenous injection ofrecombinant AAV vectors into the living mouse. The luciferase expressionwas measured 14 days after systemic injection of 5×10¹⁰ vector genomesusing the IVIS® 200 Imaging System. A: vectors on the basis of theunmodified AAV2 wild-type capsid show gene expression predominantly inthe liver. There is no measurable gene expression in the brain. Incontrast, the recombinant AAV vector rAAV2-NRGTEWD (SEQ ID NO:1) inducesa strong and specific gene expression in the brain.

FIG. 4 shows a long-term expression analysis in mouse after systemicadministration of recombinant rAAV2-NRGTEWD (SEQ ID NO:1) vector.Repeated measurements using the IVIS® 200 Imaging System exhibit stablegene expression in the brain over a period of 168 days (n=2).

FIG. 5 shows the results of the determination of luminescence and vector14 days after intravenous injection of 5×1010 vector genomes of therecombinant AAV vector rAAV2-NRGTEWD (SEQ ID NO:1). A: Measuring geneexpression as bioluminescence in the lysates of different organs of themouse showed a high specificity of the vector for the brain. B:Measuring the distribution of vector genomes in the lysates showed asignificant accumulation of the vector in the brain. Mean values +standard deviation. Statistics were calculated by one-way ANOVA.p<0.05=*; p<0.01=**; p<0.001=*** for n=3.

EXAMPLES

All data was determined as mean values + standard deviation (SD). Thestatistical analysis was performed using the GraphPad Prism 3.0 program(GraphPad Software, San Diego, USA). Data was analyzed by one-way ANOVAfollowed by multiple comparison tests as per Bonferroni. P values>0.05were considered significant.

Example 1: Selection of AAV2 Peptide Libraries

For the selection of tissue-specific AAV2 capsids, a random peptidelibrary was prepared and selected in five rounds. A random X₇-AAVpeptide library with a theoretical diversity of 1 ×10⁸ individuallyoccurring clones was prepared using a two-stage protocol as previouslydescribed [26-27]. A degenerate oligonucleotide was first produced whichcodes for seven randomized amino acids at nucleotide position 3967 inthe AAV genome, which corresponds to the amino acid position R588 inVP1. The oligonucleotide had the sequence: 5′-CAGTCGGCCAGAGAGGC(NNK)₇GCCCAGGCGGCTGACGAG-3′ (SEQ ID NO:12). The second strand wasproduced using a Sequenase (Amersham, Freiburg, Germany) and the primerwith the sequence 5′-CTCGTCAGCCGCCTGG-3′ (SEQ ID NO:13). Thedouble-stranded insert was cut with Bg1I, purified with the QIAquickNucleotide Removal Kit (Qiagen, Hilden, Germany) and ligated intolibrary plasmid pMT187-0-3 that had been digested with SfiI [26]. Thediversity of the plasmid library was determined by the number of clonesgrown from a representative aliquot of transformed, electrocompetentDH5α bacteria on agar containing 150 mg/ml ampicillin. Library plasmidswere harvested and purified by using the Plasmid Preparation Kit fromQiagen. The AAV library genomes were packaged into chimeric wild-typeand library AAV capsids (AAV transfer shuttle) by transfecting 2×10⁸293T cells in 10 cell culture dishes (15 cm) with the plasmid pVP3cm(containing the wild-type cap genes with modified codon usage withoutthe inverted terminal repeats) [27], the library plasmids and the pXX6helper plasmid [28], wherein the ratio between the plasmids was 1:1:2.The resulting AAV library transfer shuttles were used to infect 2×10⁸293T cells in cell culture dishes (15 cm) with an MOI of 0.5 replicationunits per cell. Cells were superinfected with Ad5 (provided by theLaboratoire de Therapie Génigue, France), with an MOI of 5plaque-forming units (pfu/cell). The final AAV display library washarvested from the supernatants after 48 hours. The supernatants wereconcentrated using VivaSpin columns (Viva Science, Hannover, Germany)and purified by iodixanol density gradient ultracentrifugation aspreviously described [29], and titrated by real-time PCR using thecap-specific primers 5′-GCAGTATGGTTCTGTATCTACCAACC-3′ (SEQ ID NO:14) and5′-GCCTGGAAGAACGCCTTGTGTG-3′ (SEQ ID NO:15) with the LightCycler system(Roche Diagnostics, Mannheim, Germany).

For the in vivo selection 1×10¹¹ particles of the genomic library wereinjected into the tail vein of FVB/N mice. The particles were given 8days for the distribution and the infection of the target cells. After 8days, the mice were killed and the brains were removed. The total DNA ofthe tissue was extracted using the DNeasy Tissue Kit (Qiagen). Therandom oligonucleotides that were included in AAV particles of thelibrary and had accumulated in the tissue of interest were amplified bynested PCR using the primers 5′-ATGGCAAGCCACAAGGACGATG-3′ (SEQ ID NO:16)and 5′-CGTGGAGTACTGTGTGATGAAG-3′ (SEQ ID NO:17) for the first PCR andthe primers 5′-GGTTCTCATCTTTGGGAAGCAAG-3′ (SEQ ID NO:18) and5-TGATGAGAATCTGTGGAGGAG-3′ (SEQ ID NO:19) for the second PCR. ThePCR-amplified oligonucleotides were used to prepare secondary librariesfor three additional rounds of selection. The secondary libraries weregenerated like the primary libraries (see above), but without theadditional step of producing transfer shuttles. The secondary plasmidlibrary was used to transfect 2×10⁸ 293T cells in cell culture dishes(15 cm) at a ratio of 25 library plasmids per cell, wherein thetransfection reagent Polyfect (Qiagen) was used. After each round ofselection, several clones were sequenced. The applied selection methodis shown in FIG. 1.

Results: After five rounds of selection, several brain-binding capsidswere selected. Capsids comprising the peptide sequences NRGTEWD (SEQ IDNO:1) were found to bind particularly strong to cells of the brain andspinal cord (see below). A further group of peptides, which also showedspecificity for the brain and spinal cord comprised the peptide ADGVQWT(SEQ ID NO:2), DDGVSWK (SEC ID NO:3), SDGLTWS (SEQ ID NO:4) and SDGLAWV(SEQ ID NO:5). These peptides comprised the general motif XDGXXWX (SEQID NO:6). The peptides obtained in the various rounds of selection areshown in FIG. 2.

Example 2: Preparation and Quantification of Recombinant AAV Vectors inHEK293T Cells

The clones enriched in Example 1 were produced as recombinant AAVvectors and tested for their transduction profile. Recombinant AAVvectors were produced by triple transfection of HEK293T cells. The cellswere incubated at 37° C., 5% CO₂ in Dulbecco's modified Eagle Medium(Invitrogen, Carlsbad, USA), supplemented with 1%penicillin/streptomycin and 10% fetal calf serum. Plasmid DNA wastransfected into 293T cells with the transfection agent Polyfect(Qiagen, Hilden, Germany). Four days after transfection, the cells wereharvested and lysed, and the vectors were purified by means of iodixanoldensity gradient ultracentrifugation as previously described [29]. Forthe transfections, pXX6 was used as adenoviral helper plasmid [28],which encodes the luciferase gene pUF2-CMV-luc [27] or the GFP genepTR-CMV-GFP [30], as was a plasmid encoding the AAV capsid of interest.The plasmids encoding the AAV capsid mutants which had been previouslyselected from the AAV library, and wild-type controls, were modifiedpXX2-187 [31] or pXX2 [28]. The inserts were processed as described intolibrary inserts (see above). To quantify the recombinant vectors, thegenomic titer was determined by the LightCycler system, as previouslydescribed [32], by real-time PCR using the CMV-specific primers5′-GGCGGAGTTGTTACGACAT-3′ (SEQ ID NO:20) and 5′-GGGACTTTCCCTACTTGGCA-3′(SEQ ID NO:21).

Results: It was found that the yield with respect to virus titer forrecombinant viruses with luciferase reporter gene was comparable to thatof vectors which comprised a wild type AAV2 capsid which indicates thatthe accumulated peptides do not affect the assembly of the capsid or thepackaging of the gene.

Example 3: Examination of the Tropism of the Recombinant AAV Vectors InVivo

To be able to examine the tropism of the enriched peptides in vivo, thepeptides were introduced into the capsid of a recombinant vectorcomprising a luciferase reporter gene. Vectors with mutated capsids wereinjected into mice along with control vectors. The AAV vectors wereadministered intravenously at a dose of 5×10¹⁰ vector genomes (vg)/mouse(n=3 animals per injected AAV clone). On day 14, the animals wereanesthetized with isoflurane. The luciferase expression was analyzedusing a Xenogen IVIS200 Imaging System (Caliper Lifescience, Hopkinton,USA) with the Living Image 4.0 (Caliper) software, followingintraperitoneal injection of 200 μl of luciferin substrate (150 mg/kg,Xenogen) per mouse. Representative, in vivo bioluminescence images ofthe expression of the transgene at different positions (ventral, dorsal,lateral) were taken when the luminescence in relative light units(photons/sec/cm²) reached the highest intensity.

Then the animals were sacrificed, the organs of interest were removedquickly, and images of the expression of the transgene in individualorgans were immediately taken. The organs were then frozen in liquidnitrogen and stored at −80° C. To quantify the luciferase expression,the organs were homogenized in reporter lysis buffer (RLB, Promega,Madison, USA). The determination of the luciferase reporter geneactivity was carried out in a luminometer (Mithras LB9 40, BertholdTechnologies, Bad Wildbad, Germany) at 10-second intervals after theaddition of 100 μl luciferase assay reagent (LAR, Promega), with a2-second delay between each of the measurements. The values werenormalized in each sample with respect to the total amount of proteinusing the Roti NanoQuant protein assay (Roth, Karlsruhe, Germany).

Results: The in vivo measurement of bioluminescence after 14 days showedthat the peptide NRGTEWD (SEC ID NO:1) led to an expression of thetransgene in the brain (≤10⁴ p/sec/cm²/r). These results were confirmedby the control experiments carried out ex vivo with explanted organs. Arandomly selected control clone of the non-selected library (CVGSPCG)(SEQ ID NO:43) led to a weak gene expression that occurred primarily inthe heart and in some parts of the abdomen, but not in the brain (notshown). Wild-type AAV2 caused a weak gene expression in the heart, liverand skeletal muscle, but not in the brain (FIG. 3A).

The examination of the luciferase activity of tissue lysates fromrepresentative organs revealed that the vectors which comprised thebrain-specific NRGTEWD (SEQ ID NO :1) capsid led to a strong andspecific gene expression in the brain (1.1×10⁷ RLU/mg protein, see FIG.5A). In other organ tissues, the NRGTEWD (SEQ ID NO:1) luciferase vectorhardly showed expression.

The results further showed that The brain-specific expression of thetransgene mediated by the NRGTEWD (SEQ ID NO:1) vector remainedorgan-specific over a long period. After intravenous administration ofthe AAV2 NRGTEWD (SEQ ID NO:1) luciferase vectors, the expression of thetransgene was measured over a period of 168 days. The radiation emittedin the brain region was determined quantitatively. Over the entireperiod of time, the expression of the transgene was stable at a highlevel, and was limited to the brain (FIG. 4).

Example 4: Analysis of the Vector Distribution

In order to check whether the brain-specific expression of the transgeneof intravenously injected NRGTEWD (SEQ ID NO:1) vectors is based on aspecific homing, first the distribution of vectors was investigated 14days after intravenous administration of 5×10¹⁰ gp/mouse. Thequantification of the vector genomes was performed by real-time PCR.First, the total DNA was extracted from the organ concerned at varioustime points after intravenous administration of 5×10¹⁰ vg/mouse using atissue homogenizer (Precellys 24, Peqlab, Erlangen, Germany) and theDNeasy Tissue Kit (Qiagen, Hilden, Germany) according to themanufacturer's instructions. The DNA was quantified using aspectrophotometer (NanoDrop ND-2000C, Peqlab). The analysis of the AAVvector DNA in the tissues was performed by quantitative real-time PCRusing the above-described CMV-specific primer, wherein 40 ng of templatewere used, normalized with respect to the total DNA.

Results: The quantification of the vector genomes by real-time PCRshowed a brain-specific homing of NRGTEWD (SEQ ID NO:1). The amount ofvector genomes which could be detected in the brain (1.6×10⁴±7.1×10³vg/100 ng total DNA) was significantly higher than the amount of vectorgenomes which was detected in another organ (FIG. 5B). To determine thedirect correlation between vector homing and expression of thetransgene, the vector distribution of wild-type AAV2, the controlpeptide CVGSPCG and the brain-specific peptide NRGTEWD (SEQ ID NO:1) wasmeasured 14 days after intravenous administration of 5×10¹⁰ gp/mouse,i.e., at the time when the expression of the transgene was determined(see above). The genomes provided by wild-type AAV2 vectors were mainlyrecovered from the liver and spleen, and the genomes of vectors whichhad the control peptide were obtained largely from the spleen (data notshown). In total, the amount of vector genomes which were detected inthe spleen were relatively equal in all examined capsid variants,suggesting a non-specific capture mechanism for the particles in thereticulo-endothelial system which is independent of the provision andthe expression of the transgene. In contrast, the distribution data ofgenomes which were provided by vectors which had the brain-specificpeptide NRGTEWD (SEQ ID NO:1) was highly similar to the expression dataof the transgene, with a highly specific accumulation observed in thebrain. The amount of vectors detected in the brain which showed thepeptide NRGTEWD (SEQ ID NO:1) was about 168-fold higher than in brains,which were injected with a wild-type vector or a control capsid vector.Overall, this data indicates that a brain-specific expression of thetransgene, mediated by NRGTEWD (SEQ ID NO:1) vectors, is achieved by atissue-specific homing of circulating particles.

Example 5: Immunohistochemistry and Histology

Immunohistochemistry was used to visualize the expression of thetransgene at the cellular level in the brain, as well as in a controlorgan, 14 days after the intravenous administration of the rAAV-GFPvector having the peptide NRGTEWD (SEQ ID NO:1) and/or the wild-type AAVcapsid as control. The brains of the animals were fixed with 4% (w/v)paraformaldehyde. The tissues were embedded in paraffin. Sections with athickness of 2 μm were removed from wax, rehydrated and used forimmunohistochemistry. An immunohistochemical procedure was performedusing polyclonal antibodies for GFP (A-11122, Invitrogen) or CD31(AB28364, Abcam, Cambridge, USA). The activity of the endogenousperoxidase was inactivated with 1% H₂O₂ in methanol for 30 minutes.Prior to staining with CD31, the sections were heated in citrate buffer(pH 6.0) for 20 minutes at 100° C. After washing in PBS, the sectionswere incubated for 30 minutes with PBS, 10% goat serum (Vector Lab,Burlingame, USA) and 2% milk powder (Roth). Primary antibodies wereallowed to bind for 1 hour at 37° C. After washing in PBS, the sectionswere incubated for 30 minutes with a secondary, biotinylated goatanti-rabbit antibody (Vector Lab). Bound antibodies were visualized byusing the VECTASTAIN-Elite ABC kit (Vector Lab) and3,3′-diaminobenzidene (DAB, Sigma-Aldrich, St. Louis, USA). Selectedsections were counterstained with Hemalum.

Results: In the brains of mice injected with rAAV-NRGTEWD (SEQ ID NO:1),a microscopic examination showed intensive staining of the endothelialcells over the entire microvasculature and to a slightly lesser extentin the large vessels (data not shown). In contrast, brain tissue of micewhich was injected with wild-type AAV2 vector showed no staining. Toconfirm the tissue specificity, the liver was analyzed as a controlorgan (a tissue which is known to frequently demonstrate high expressionof a transgene after injection of wild-type AAV2 vector). In the liver,hepatocyte staining was observed after administration of wild-type rAAV2vector; but no staining was observed after administration ofrAAV2-NRGTEWD (SEQ ID NO:1) vector. The endothelial lineage of cellstransduced with the vectors was confirmed by CD31 staining, wherein thepattern obtained by the GFP staining was confirmed in serial sections ofthe brains of mice injected with rAAV2-NRGTEWD(SEQ ID NO:1) (data notshown).

The examination of the spinal cord of mice which have been injected withrAAV-NRGTEWD (SEQ ID NO:1) also revealed an intensive staining of theendothelial cells of the microvasculature which shows that not only theendothelial cells of the brain but rather the endothelial cells of thecomplete central nervous system are transducable with the peptides ofthe invention (data not shown).

Example 6: Production and Quantification of Recombinant AAV VectorsUsing the Baculovirus Expression System in Sf9 Insect Cells.

For the production of recombinant AAV vectors in Sf9 insect cells[33-35] the modified AAV2 genome having the oligonucleotide insert inthe cap gene which encodes the peptide insertion (see above) was clonedinto the donor plasmid pFASTBAC Dual (Life Technologies, Darmstadt,Germany). In addition, an artificial intron was inserted into the donorplasmid which included the polh promoter, thereby giving plasmidpFBD-Rep_(in)/Cap_(in) [35]. For establishing the donor plasmidpFB-CAG-eGFP, the CAG promoter and the eGFP gene were cloned togetherwith the SV40 polyadenylation signal and the AAV2 ITRs into plasmidpFASTBAC1 (Life Technologies). The donor plasmids were used fortransforming DH10Bac E. coli cells which were subsequently used forisolating recombinant bacmids that comprised the recombinant AAV genomeor the eGFP transgene cassette, respectively. The bacmids (9 μg) wereused for transfection of 1 ×10⁶ Sf9 cells using theFectofly-Transfektionreagenz (Poly-plus Transfection/VWR InternationalGmbH, Darmstadt, Germany) in a 6-well format. After 3 days of incubationof the transfected Sf9 insect cells at 27° C. in insect X-Press Medium(Lonza, Cologne, Germany) with 1% Gentamycin (Lonza), 500 μl of therecombinant baculoviruses present in cell culture supernatants were usedfor the amplification of 2.5×10⁷ fresh Sf9 cells in T175 cell cultureflasks for additional 3 days at 27° C. in Insect X-Press Medium (Lonza)with 1% Gentamycin. The baculoviruses amplified in this way were usedfor infecting fresh Sf9 cells for producing recombinant AAV vectors. Forthis purpose, recombinant baculovirus with inserted AAV genome andrecombinant baculovirus with inserted eGFP transgene cassette were mixedand used together in 400 ml Insect X-Press Medium with 1% Gentamycin ina 1 L Erlenmeyer flask for infecting 6×10⁸ insect cells. The cells weresubsequently incubated at 27° C. under agitation (110 rpm). 4 days afterinfection, the cells were harvested, lysed, and the AAV vectors werepurified via iodixanol gradient ultra centrifugation as described before[29]. For quantification of the recombinant vectors, the genomic titerwas determined by quantitative real time PCR using the CMV specificprimer of SEQ ID NO:20 and SEQ ID NO:21 in the LightCycler system asdescribed before [32].

Results: By using the baculovirus expression system, higher titers ofrecombinant AAV vectors were achieved in Sf9 insect cells compared tothe production in HEK293T cells after triple transfection. While theyield of virus production in HEK293T cells had a maximum of 1.9×10⁴genomic particles per cell, a yield of up to 7.9×10⁴ genomic particlesper cell were observed in Sf9 insect cells. It could further be observedthat rAAV2-NRGTEWD (SEQ ID NO:1) vectors produced in Sf9 insect cellshad a higher affinity for neurons than comparable recombinant vectors,which have been produced in HEK293T cells (data not shown). Thus, thechoice of the specific production process for the recombinant vectorsprovides the possibility of increasing the specificity of the vectorsfor the neuron or endothelial cells, respectively.

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The invention claimed is:
 1. A capsid protein of a viral vectorcharacterized in that it comprises the amino acid sequence of SEQ IDNO:1.
 2. The capsid protein according to claim 1, which is a capsidprotein of an adeno-associated virus (AAV).
 3. The capsid proteinaccording to claim 2, which is a capsid protein of an AAV of a serotypeselected from the group consisting of serotypes 2, 4, 6, 8, and
 9. 4.The capsid protein according to claim 3, which is a capsid protein of anAAV of serotype
 2. 5. The capsid protein according to claim 4, which isa VP1 protein of an AAV of serotype
 2. 6. The capsid protein accordingto claim 1, comprising the amino acid sequence of SEQ ID NO:10.
 7. Acell which comprises a capsid protein according to claim
 6. 8. Apharmaceutical composition which comprises a capsid protein according toclaim
 6. 9. A method for the targeted delivery of viral vectors to thebrain and/or spinal cord in a subject, comprising administering a capsidprotein according to claim 6 to the subject.
 10. A viral capsid whichcomprises the capsid protein according to claim
 1. 11. A cell whichcomprises a capsid protein according to claim
 1. 12. A pharmaceuticalcomposition which comprises a capsid protein according to claim
 1. 13. Amethod for the targeted delivery of viral vectors to the brain and/orspinal cord in a subject, comprising administering a capsid proteinaccording to claim 1 to the subject.
 14. A nucleic acid which encodes acapsid protein characterized in that the capsid protein comprises theamino acid sequence of SEQ ID NO:1.
 15. A plasmid which comprises anucleic acid according to claim
 14. 16. The nucleic acid of claim 14,characterized in that the capsid protein comprises the amino acidsequence of SEQ ID NO:1.
 17. A recombinant viral vector which comprisesa capsid and a transgene packaged therein, wherein the capsid comprisesat least one capsid protein, characterized in that the capsid proteincomprises the amino acid sequence of SEQ ID NO:1.
 18. The recombinantviral vector according to claim 17, which is a recombinant AAV vector.19. The recombinant viral vector according to claim 18, which is an AAVvector of a serotype selected from the group consisting of serotypes 2,4, 6, 8, and
 9. 20. The recombinant viral vector according to claim 19,which is an AAV vector of serotype
 2. 21. The recombinant viral vectoraccording to claim 17, wherein the transgene encodes one of thefollowing proteins: a membrane or tight junction protein, aneuraminidase, glucuronidase, a chemokine antagonist, neurotrophicfactor of glia cells (GDNF), neprilysine, cholesterol 24 hydroxylase,aromatic L-amino acid decarboxylase, a tyrosine hydroxylase, GTPcyclohydrolase I, and survival of motor neuron (SMN) protein.
 22. Therecombinant viral vector according to claim 21, wherein the transgeneencodes a neuraminidase.
 23. The recombinant viral vector according toclaim 21, wherein said membrane or tight junction protein is a claudinor occludin.
 24. The recombinant viral vector according to claim 21,wherein said neuraminidase is neuraminidase
 1. 25. The recombinant viralvector according to claim 21, wherein said chemokine antagonist isCCL2-7ND.
 26. The recombinant viral vector according to claim 17,wherein the transgene is in the form of an ssDNA or a dsDNA.
 27. Amethod for the targeted delivery of viral vectors to the brain and/orspinal cord in a subject, comprising administering a recombinant viralvector according to claim 17 to the subject.
 28. The method according toclaim 27, wherein the subject is a mammal.
 29. The method according toclaim 28, wherein the mammal is a human.
 30. The method according toclaim 27, wherein the vector is formulated for intravenousadministration.
 31. A pharmaceutical composition which comprises a viralvector according to claim
 17. 32. A recombinant viral vector whichcomprises a capsid and a transgene packaged therein, wherein the capsidcomprises at least one capsid protein, characterized in that the capsidprotein comprises the amino acid sequence of SEQ ID NO:10.
 33. Therecombinant viral vector according to claim 32, which is an AAV vectorof serotype
 2. 34. The recombinant viral vector according to claim 32,wherein the transgene encodes one of the following proteins: a membraneor tight junction protein, a neuraminidase, glucuronidase, a chemokineantagonist, neurotrophic factor of glia cells (GDNF), neprilysine,cholesterol 24 hydroxylase, aromatic L-amino acid decarboxylase, atyrosine hydroxylase, GTP cyclohydrolase I, and survival of motor neuron(SMN) protein.
 35. The recombinant viral vector according to claim 34,wherein the transgene encodes a neuraminidase.
 36. The recombinant viralvector according to claim 34, wherein said membrane or tight junctionprotein is a claudin or occludin.
 37. The recombinant viral vectoraccording to claim 34, wherein said neuraminidase is neuraminidase 1.38. The recombinant viral vector according to claim 34, wherein saidchemokine antagonist is CCL2-7ND.
 39. The recombinant viral vectoraccording to claim 32, wherein the transgene is in the form of an ssDNAor a dsDNA.
 40. A method for the targeted delivery of viral vectors tothe brain and/or spinal cord in a subject, comprising administering arecombinant viral vector according to claim 32 to the subject.
 41. Themethod according to claim 40, wherein the subject is a mammal.
 42. Themethod according to claim 40, wherein the mammal is a human.
 43. Themethod according to claim 40, wherein the vector is formulated forintravenous administration.
 44. A pharmaceutical composition whichcomprises a viral vector according to claim 32.